In the Gather process, traces from different shot gathers are rearranged as a CMP gathers.
At distance from the source, the tops of records commonly have unwanted noise (direct P- and S waves, refraction events distorted by Tnmo corrections), with few or no reflections. Rather than stack this noise together with reflections recorded near the source, a (commonly triangular) region of CMP gather traces are set to zero amplitude, or muted. On the tops of actual seismic reflection profiles, including many of those in chapter 6, can be see as V-shaped “valleys” in regions where only far offsets comprise the stack traces.
Introduction to Geophysics Ali Oncel [email_address] Department of Earth Sciences KFUPM Seismic Reflection 3: Acquisiton, Processing, and Waveform Analysis Introduction to Geophysics-KFUPM
Shaybah Field: Data Acquisition Introduction to Geophysics-KFUPM Alfaraj et al., 1998, GeoArabia, Vol. 3, No 2 .
correct V NMO is one which flattens the reflection hyperbola Introduction to Geophysics-KFUPM Uncorrected CMP gather Correct velocity (224 m/s) Overcorrection: velocity too low (2000 m/s) Undercorrection: velocity too high (2500 m/s)
Introduction to Geophysics-KFUPM Gathers and NMO Corrected CMP
Introduction to Geophysics-KFUPM NMO Corrections